Thirty-eight cases of subacute sclerosing panencephalitis (SSPE) were reviewed. Deterioration in school performance, personality changes, and seizures were common early symptoms. Initial examination frequently showed myoclonus, spasticity, and extrapyramidal dysfunction, and in two-thirds of patients these findings were asymmetrical or focal. Retinitis or papilledema was present on initial examination in 50% of the patients. At last follow-up 24 children had died, with a mean survival of 42 months. Most patients reached a state of severe neurological impairment within 13 months. Subsequent evidence of improvement was noted in 10 children and was sustained in 4. Fifteen patients received antiviral treatment. Ten treated patients died from 5 to 133 months (mean, 58) from onset of their illness, while 15 untreated patients survived a mean of 33 months. Duration of survival appeared to be affected most by treatment with amantadine. Three patients treated with the drug were alive 97 to 139 months after onset of SSPE, and 5 died with a mean survival of 78 months. Five of 6 individuals treated with rifampin died after a mean survival of 27 months. Prolonged remissions occurred only in patients treated with amantadine. Although the number of treated individuals was small, our data suggest that amantadine may affect the natural course of SSPE.